I understand that you want a false bottom. That being said, I'd go with the manifold approach.
If you're set on a false bottom, though.....
Measure the dimension of your MLT approximately 1 inch from the bottom. Find a suitable rectangle of plastic/ plexiglass/ aluminum/ stainless.
Drill, drill, drill until you have enough holes to suit you. Add legs to give it stability.
It really shouldn't be a problem to make one. Good luck trying to buy one. I'd just go with the manifold.
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